The field of medical engineering is rapidly expanding due to advances in engineering, material science, and advances in the field of medicine. These advances have allowed doctors and engineers to work together to create instruments and devices that allow more accurate and effective diagnosis and treatment of a wide variety of ailments. The diagnoses and treatments enable patients to recover from injuries or diseases that used to be crippling, or even fatal.
One area of the human body that is of particular importance is the skeletal system. Advances in medical engineering and medicine have allowed doctors to treat a wide variety of ailments involving the skeletal system, including back, neck, and joint pain. In addition, advancements have allowed faster healing of breaks and fractures of bones. Of particular importance are breaks or fractures of the spinal cord, because they can result in severe pain or even paralysis.
One common method of fixing broken or fractured bones is through the use of a fixation device. Typically, this involves a screw or a nail being inserted into the bone. Often, the screw or nail functions to anchor other components of a medical device to the bone. Additionally, a fastener and fixation device may be used to join two parts of a bone, or to hold two bones together. For example, bone screws may be used in a spinal fixation system to immobilize two or more vertebrae. These fixation devices can be used in conjunction with other devices or components, such as plates that hold the bones together and prevent movement.
Despite the advances in medical engineering, fixation and other devices are susceptible to the inherent weaknesses of bones and other bony tissue. Further complicating the matter, bones may become weak, brittle, or lose strength for a number of reasons. For example, the patient's age and nutrition may be factors for bone strength. Additionally, the strength of the bones may vary based on the degree of damage to the bone from disease, trauma, or the like. As the structure or strength of a bone lessens, it becomes increasingly difficult to use it for placement of a fastener. Thus, a bony anatomy capable of receiving and securely holding a fastener when healthy may not be sufficiently strong enough to resist pressure from a screw head when in a weakened state. Because a fixation device requires penetration of the bone, the strength of the bone has to be considered. The insertion of fixation devices, such as screws, often requires the drilling of holes into the bone. As the head of the fastener contacts the bony anatomy, it can impart a localized concentration of stress or pressure that a weakened bone may not be able to withstand. The exertion of a significant load on a small area of the bone may cause it to chip, crack, fracture, collapse, or break.
When fixation devices are used in spinal applications, the movement of the vertebrae must also be taken into consideration. A significant problem with screws that are inserted into vertebrae is that they tend to “backout,” or unscrew due to the motion of the bones. When a screw backs out, it can require additional invasive procedures in order to correct the problem. In addition, because vertebrae vary in shape and size, they are particularly susceptible to breaking or cracking.
A continuing need exists for a load distribution device that is able to accommodate screws at various angles of insertion. Furthermore, a need exists for a load distribution device that is able to prevent backing out of a fixation device and reduce the likelihood of undesired chipping, cracking, fracturing, or breaking of the bone when the fixation device is being inserted.